1. Technical Field of the Invention
The present invention relates to co-channel wireless communications systems and, in particular, to addressing coexistence problems causing harmful interference amongst such co-channel wireless communications systems.
2. Description of Related Art
Reference is now made to FIG. 1 wherein there is schematically illustrated coexisting co-channel wireless communications systems. A first wireless communications system 10 provides a service A from a broadcast station 12 on a certain channel K. The service A is a “protected wireless telecommunication service.” By this it is meant that the channel K on which service A is provided is reserved for Service A within a predetermined range (distance) of the broadcast station 12 without competition or interference from other services. An example of a protected service such as service A would include a television (TV) broadcast service or an FM radio broadcast service.
A second wireless communications system 20 provides a service B from a broadcast station (base station) 22 on a selected one or more of a plurality of channels, wherein a selectable one of the channels includes the certain channel K used by service A. The service B is typically not a protected wireless telecommunication service. Service B must obey at least the following rule with respect to service A: service B cannot make a harmful intrusion to any protected service such as service A. This means that service B is allowed to use (operate on) channel K, which is also being used by service A, only when such operation will not cause a harmful interference to service A. If such a harmful interference arises with respect to the protected service A, service B is obligated to leave channel K immediately. It is the responsibility of service B, or the person/entity who provides service B, to ensure that the foregoing rule against interfering with protected service A is not being violated. An example of a non-protected service such as service B would include a point-to-multipoint wireless telecommunication network (such as an IEEE P802.22 Wireless Regional Area Network (WRAN)).
With respect to a typical point-to-multipoint wireless telecommunication network (such as an IEEE 802.22 WRAN), the base station (BS) 22 manages operation of the established wireless network in communication with proximate network members. In this regard, it is the responsibility of the base station 22 to determine which of the plurality of channels is selected as the working channel, as well as how communication opportunities are allocated to the members of the network. It is accordingly the responsibility of the base station 22 to monitor the spectrum situation, detect the harmful intrusion to the protected service A and if such interference occurs, command all the members of its network to leave the current working channel K for another working channel.
One known mechanism for spectrum monitoring by the base station involves providing an interference detection capability within the base station 22 itself. The interference detection capabilities of the base station 22 are, however, limited. Thus, there exists a detection problem with respect to the use of the base station 22, since in some situations the base station 22 may not be able to discover all instances of harmful interference to protected service A.
Another known mechanism for spectrum monitoring by the base station involves the use of the members of the network. In this solution, the members of the network monitor for interference on channel K and make reports back to the base station 22. For example, each network member operating on the working channel monitors the current interference situation and where an unacceptable level of interference is found, the member sends a report to the base station 22 to inform the base station about this interference. The base station 22 collects the detection reports from its network members and processes the reports to determine whether the rule against interfering with service A is being violated (for example, because protected service A has been assigned to use working channel K). Thus, in this mechanism the base station 22 of service B at least partially depends on its network members to detect instances of harmful intrusion on or to protected services.
In connection with the network member mechanism, it will noted that in the absence of effective network members in a position to monitor for interference and generate reports back to the base station 22, the base station 22 will potentially be unaware of its harmful intrusion on or to the protected service A. This is referred to as the “blind base station” problem since the base station is blind to the fact that its choice of channel K is potentially interfering with service A's use of channel K. A better understanding of how this problem occurs may be obtained by reference to FIG. 1.
Consider first the existence of two service B network members 24 and 26 which are positioned within the noise limited contour 28 of the service B base station 22. Network member 24 receives service B outside of the service A coverage area 30 (i.e., the area where service A can be sensed by, for example, network members for service B). Thus, network member 24 will not sense interference from service A and thus will not be in a position to discover and make an interference report regarding channel K to the base station 22. With respect to network member 26, however, it receives service B within the service A coverage area 30. At this location, network member 26 is positioned to sense interference from service A and thus can make interference reports regarding channel K to the base station 22. In this situation, the base station 22 is not blind because at least one network member (i.e., network member 26) is positioned within the noise limited contour 28 of service B such that it can detect interference from service A and make appropriate reports to the base station 22. The base station 22, in response to the interference reports from network member 26, can determine or infer that the rule against interfering with service A is being violated by its co-use of channel K and act to move service B off of the co-channel K.
Assume now that there are no network members (such as network member 26 in the foregoing example) which are positioned both within the noise limited contour 28 of service B and the service A coverage area 30 (see, shaded region 32). Or alternatively, that such network members are present in region 32 but are not operating properly at least with respect to the functionality for detecting interference. The service B has a coverage area 34 (i.e., the area where service B can be sensed by, for example, network members for service A) which overlaps with the service A coverage area 30 and further, and more importantly, overlaps with the noise limited contour 36 of the service A broadcast station 12 (see, shaded region 38). Consider now a service A receiver 40 located within the shaded region 38. This receiver 40 will have its service A reception interfered with by service B communications (due to the overlapping service B coverage area 34). However, because service B has no network members located within the shaded region 32 (or the members are not operating properly to detect interference), the base station 22 will not receive any network member reports of interference and is thus blind to the potential or actual interference it is causing to the protected service A in the shaded region 38.
In general, the blind base station problem exists when each of the following four conditions are met at the same time: 1. service B and service A work on the same channel (such as channel K) at the same time; 2. the service B coverage area 34 overlaps with the service A noise-limited contour 36 (i.e., the radius of service B's coverage area plus the radius of service A's noise limited contour exceeds the distance between the two broadcast/base stations); 3. the service B base station is outside of the service A coverage area 30 (i.e., the distance between the two broadcast/base stations is greater than the radius of service A's coverage area); and 4. there is no service B network member (or such member is not working properly) in the overlapping zone (region 32) between service B's noise-limited contour 28 and service A's coverage area 30.
A need accordingly exists in the art to address the blind base station issue which can arise in connection with coexisting services provided by co-channel wireless telecommunication systems.